Front projection screens including reflective layer and an array of anamorphic microlenses

ABSTRACT

Projection screens include a substrate, a reflective layer on the substrate and a refractive layer on the substrate. The refractive layer includes an array of anamorphic microlenses.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of application Ser. No. 11/179,162,filed Jul. 12, 2005, now U.S. Pat. No. 7,324,276, entitled FrontProjection Screens Including Reflecting And Refractive Layers OfDiffering Spatial Frequencies, assigned to the assignee of the presentapplication, the disclosure of which is hereby incorporated herein byreference in its entirety as if set forth fully herein.

FIELD OF THE INVENTION

This invention relates to optical structures and fabrication methodstherefor, and more specifically to front projection screens andfabrication methods therefor.

BACKGROUND OF THE INVENTION

Front projection screens, also referred to as reflective- orreflection-type projection screens, are widely used in cinemas, hometheaters and other consumer and commercial applications, wherein aprojector is on the same side of the projection screen as the viewer(s).

In designing a front projection screen, it may be desirable to providehigh brightness, an acceptable viewing angle (light distribution), colorrendition and/or contrast. Many screen designs have been developed thatcan improve projected image quality over a simple “white wall”.

Front projection screens that are used in cinema or home theaterapplications generally are viewed in dark or subdued lightingconditions. Accordingly, many commercially available screens may lack anability to effectively reduce or eliminate ambient light reflection thatproduces loss of contrast and causes the image to wash out in brightlylit settings. One approach to improve the effective contrast of a frontprojection screen is to increase its gain, or on-axis brightness. Highgain can provide a larger ratio of reflected image light to reflectedambient light in a given setting. This may perceived by the viewer in anumber of ways, including brighter whites, deeper blacks, more pleasingcolor saturation, improved edge definition and/or improved picturedetail.

Unfortunately, high gain screens may reduce the viewing angle of thescreen. Stated differently, high on-axis brightness may be achievedthrough reduction and brightness at other angles. Thus, for a givenprojector with a given lumen output, a high gain screen may have asmaller field of view than a low gain screen. In order to allow arelatively wide field of view, many commercial projection screens offeronly a modest increase in gain over a white wall.

U.S. Pat. No. 6,724,529 to Sinkoff, entitled “Reflection-Type ProjectionScreens”, describes a projection screen comprising; a substrate having agenerally flat forward surface; a diffusion layer formed of a pluralityof generally equally spaced apart concave features forming micro lenses;a layer of reflective material deposited on a rearward facing surface ofthe diffusion layer; the diffusion layer laminated to the forward facingsurface of the substrate so that the layer of reflective material issandwiched therebetween. See the abstract of U.S. Pat. No. 6,724,529.

SUMMARY OF THE INVENTION

Projection screens according to exemplary embodiments of the presentinvention include a substrate, a reflective layer on the substrate and arefractive layer on the substrate. The reflective layer comprisesreflective microstructures of about 0.5 μm to about 500 μm in size, andarranged in a first pattern to reflect light at a first spatialfrequency. The refractive layer comprises refractive microstructures ofabout 0.5 μm to about 500 μm in size, and arranged in a second patternthat is different from the first pattern, to refract light at a secondspatial frequency that is different than the first spatial frequency.

As is well known to those having skill in the art, spatial frequencyrefers to the inverse of the periodicity with which the image intensityvalues change. Small objects generate high spatial frequencies whilelarge objects generate low spatial frequencies. As used herein,reflecting or refracting light at a given spatial frequency includesfrequencies below and up to the given spatial frequency, but not abovethe given spatial frequency. Moreover, the first and second differentpatterns can differ in size, shape and/or any other characteristic ofthe elements of the pattern.

In some embodiments, the reflective microstructures are between about 1μm and about 100 μm in size, and the refractive microstructures arebetween about 1 μm and about 100 μm in size. Moreover, in someembodiments, the first and second patterns are randomly and/or regularlyarranged.

In some embodiments, the projection screen has a front and a back, andthe reflective layer and the refractive layer are arranged on thesubstrate, such that light that is projected to the front of theprojection screen passes through and is refracted by the refractivelayer, to impinge on the reflective layer, and is reflected from thereflective layer back through the refractive layer to emerge from thefront of the projection screen. In still other embodiments, theprojection screen has a vertical axis and a horizontal axis, and thereflective layer and/or the refractive layer are configured to produce avertical half angle of the light that emerges from the front of theprojection screen that is less than a horizontal half angle of the lightthat emerges from the front of the projection screen. As is well knownto those having skill in the art, half angle denotes the angle fromnormal to the screen at which the light intensity reaches half of itson-axis intensity. Twice the half angle also may be referred to as aFull Width at Half Maximum (FWHM) angle.

In still other embodiments of the present invention, the first patterncomprises a plurality of grooves that extend along the vertical axis,and the refractive microstructures comprise a plurality of anamorphicmicrolenses having a vertical half angle that is less than a horizontalhalf angle thereof. As is well known to those having skill in the art,an anamorphic lens is a non-rotationally symmetric lens that may resultin broader divergence in one direction than in another direction.Moreover, in other embodiments, the anamorphic microlenses are on thefirst face and the plurality of grooves are between the refractive layerand the first face.

In still other embodiments of the invention, the first pattern comprisesa texture pattern, and the refractive microstructures comprise an arrayof anamorphic microlenses. In some of these embodiments, the substrateincludes first and second opposing faces, the refractive layer is on thefirst face, and the reflective layer is between the refractive layer andthe first face. In other embodiments, the refractive layer is on thefirst face and the reflective layer is on the second face.

In still other embodiments, the first pattern comprises a plurality ofanamorphic reflectors having a vertical half angle that is less than ahorizontal half angle thereof, and the refractive microstructurescomprise a plurality of anamorphic microlenses having a vertical halfangle that is less than a horizontal half angle thereof. In still otherembodiments, the plurality of anamorphic microlenses are on the firstface, and the plurality of anamorphic reflectors are on the second face.In still in other embodiments, one of the reflective layer or therefractive layer is configured to preferentially reflect or refractlight along the horizontal axis, compared to the vertical axis. Theother of the reflective layer or the refractive layer is configured topreferentially reflect or refract light along the vertical axis comparedto the horizontal axis.

In still other embodiments, the refractive layer is a first refractivelayer, and the projection screen further comprises a second refractivelayer on the substrate. The second refractive layer comprises refractivemicrostructures of about 0.5 μm to about 500 μm in size, and arranged inthe first pattern. In these embodiments, the reflective layer extendsconformally on the second refractive layer. Moreover, in someembodiments, the first refractive layer is on the first face of thesubstrate, the second refractive layer is on the second face of thesubstrate, and the reflective layer is on the second refractive layeropposite the second face.

Projection screens according to other exemplary embodiments of thepresent invention comprise a substrate including a reflective metal facehaving a textured surface, to provide reflective microstructures ofabout 0.5 μm to about 500 μm in size, and arranged in a first pattern toreflect light at a first spatial frequency. An array of refractivemicrostructures of about 0.5 μm to about 500 μm in size is provided onthe textured surface and arranged in a second pattern that is differentfrom the first pattern, to refract light at a second spatial frequencythat is different from the first spatial frequency. In some embodiments,the first pattern comprises a plurality of grooves that extend along thevertical axis and the refractive microstructures comprise a plurality ofanamorphic microlenses having a vertical half angle that is less than ahorizontal half angle thereof.

Projection screens according to yet other exemplary embodiments of thepresent invention comprise a transparent substrate having front and backfaces. A first array of refractive microstructures of about 0.5 μm toabout 500 μm in size is provided on the front face and arranged in afirst pattern to refract light at a first spatial frequency. A secondarray of refractive microstructures of about 0.5 μm to about 500 μm insize is provided on the back face and arranged in a second pattern thatis different from the first pattern, to refract light at a secondspatial frequency that is different than the first spatial frequency. Areflective layer also is provided that extends conformally on the secondarray of refractive microstructures, to provide an array of reflectivemicrostructures of about 0.5 μm to about 500 μm in size on the backface, and arranged in the second pattern to reflect light at the secondspatial frequency. In some of these embodiments, the first and secondarrays of refractive microstructures comprise respective first andsecond arrays of anamorphic microlenses having vertical half angles thatare less than horizontal half angles thereof.

Projection screens may be fabricated, according to exemplary embodimentsof the invention, by texturing a surface of a reflective metal substrateand arranging a mold of microlenses adjacent the surface that wastextured, with liquid polymer between the mold and the surface that wastextured, to thereby mold the microlenses in the liquid polymer. Theliquid polymer is then photocured and the mold is removed. In someembodiments, the above-described molding may take place by placing themold adjacent the surface that was textured and injecting the liquidphotopolymer between the mold and the surface that was textured. Inother embodiments, this molding may take place by placing the liquidphotopolymer on the surface that was textured and placing the mold onthe liquid photopolymer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross-sectional view of a front projection screen accordingto exemplary embodiments of the present invention viewed from the top ofscreen.

FIG. 1B is a cross-sectional view of a front projection screen of FIG.1A viewed from a side of the screen.

FIG. 2A is a cross-sectional view of a front projection screen accordingto other exemplary embodiments of the present invention viewed from thetop of screen.

FIG. 2B is a cross-sectional view of a front projection screen of FIG.2A viewed from a side of the screen.

FIGS. 3A and 3B are cross-sectional views of screens of FIGS. 1A and 1Bduring intermediate fabrication steps according to exemplary embodimentsof the present invention.

FIGS. 4A and 4B are micrographs of portions of a projection screenaccording to exemplary embodiments of the present invention.

DETAILED DESCRIPTION

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which embodiments of theinvention are shown. However, this invention should not be construed aslimited to the embodiments set forth herein. Rather, these embodimentsare provided so that this disclosure will be thorough and complete, andwill fully convey the scope of the invention to those skilled in theart. In the drawings, the thickness of layers and regions may beexaggerated for clarity. Like numbers refer to like elements throughout.As used herein the term “and/or” includes any and all combinations ofone or more of the associated listed items and may be abbreviated as“/”.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises,”“comprising,” “includes,” and/or “including” when used in thisspecification, specify the presence of stated features, regions, steps,operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, regions, steps,operations, elements, components, and/or groups thereof.

It will be understood that when an element such as a layer or region isreferred to as being “on” or extending “onto” another element, it can bedirectly on or extend directly onto the other element or interveningelements may also be present. In contrast, when an element is referredto as being “directly on” or extending “directly onto” another element,there are no intervening elements present. It will also be understoodthat when an element is referred to as being “connected” or “coupled” toanother element, it can be directly connected or coupled to the otherelement or intervening elements may be present. In contrast, when anelement is referred to as being “directly connected” or “directlycoupled” to another element, there are no intervening elements present.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, components, regions, layersand/or sections, these elements, materials, regions, layers and/orsections should not be limited by these terms. These terms are only usedto distinguish one element, material, region, layer or section fromanother element, material, region, layer or section. Thus, a firstelement, material, region, layer or section discussed below could betermed a second element, material, region, layer or section withoutdeparting from the teachings of the present invention. In particular, asused herein, the relative terms “first direction” and “second direction”mean two different, not necessarily orthogonal, directions, whereas theterms “horizontal” and “vertical” indicate specific orientations basedupon the ultimate orientation of the projection screen. Moreover, theterms “front” and “back” are used herein to describe opposing outwardfaces of a front projection screen. Conventionally, the viewing face isdeemed the front, but the viewing face may also be deemed the back,depending on orientation. Finally, the terms “viewing angle,” “field ofview,” “half angle” and “FWHM” are used interchangeably herein to denotea range of acceptable viewing positions that are offset from normal tothe screen.

Embodiments of the present invention are described herein with referenceto cross section illustrations that are schematic illustrations ofidealized embodiments of the present invention. As such, variations fromthe shapes of the illustrations as a result, for example, ofmanufacturing techniques and/or tolerances, are to be expected. Thus,embodiments of the present invention should not be construed as limitedto the particular shapes of regions illustrated herein but are toinclude deviations in shapes that result, for example, frommanufacturing. For example, a region illustrated or described as flatmay, typically, have rough and/or nonlinear features. Moreover, sharpangles that are illustrated, typically, may be rounded. Thus, theregions illustrated in the figures are schematic in nature and theirshapes are not intended to illustrate the precise shape of a region andare not intended to limit the scope of the present invention.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art and thepresent disclosure, and will not be interpreted in an idealized oroverly formal sense unless expressly so defined herein.

FIGS. 1A and 1B are cross-sectional views of a projection screenaccording to exemplary embodiments of the present invention, when viewedfrom the top of the screen and when viewed from a side of the screen,respectively. Thus, FIG. 1A illustrates a cross-section of a projectionscreen 100 extending along a horizontal axis H, whereas FIG. 1Billustrates a cross-sectional view along the vertical axis V.

Referring to FIGS. 1A and 1B, these embodiments of projection screens100 include a front or front face 102 and a back or back face 104,wherein the front face 102 is defined as the face that is adjacent(i.e., faces) a projector 140 and a viewer.

Still referring to FIGS. 1A and 1B, the projection screen 100 includes asubstrate 110 and a reflective layer 120 on the substrate 110. Thereflective layer 120 comprises reflective microstructures 122 of about0.5 μm to about 500 μm in size, and arranged in a first pattern, toreflect light at a first spatial frequency. It will be understood bythose having skill in the art, that the reflective microstructures 122of about 0.5 μm to about 500 μm refers to the size of the reflectivemicrostructures 122 along at least a first direction of the screen, suchas the horizontal direction in FIG. 1A. The reflective microstructuresmay be larger or smaller along at least a second direction of thescreen, such as the vertical direction of FIG. 1B. In FIG. 1A, thereflective layer 120 comprises a texture pattern, for example aplurality of grooves that extend along the vertical axis of FIG. 1B.However, other patterns of textured reflective layers also may beprovided.

Still referring to FIGS. 1A and 1B, a refractive layer 130 also isprovided on the substrate 110. The refractive layer comprises refractivemicrostructures 132, such as microlenses of about 0.5 μm to about 500 μmin size, and arranged in a second pattern that is different from thefirst pattern, to refract light at a second spatial frequency that isdifferent from the first spatial frequency. It will be understood thatthe refractive microstructures 132 of about 0.5 μm to about 500 μmrefers to the size of the refractive microstructures along at least afirst direction of the screen, such as the horizontal direction shown inFIG. 1A. The refractive layer 130 may be larger or smaller in size alonga second direction, such as along a vertical direction, for example whenlenticular lenses are used.

In other embodiments, the reflective microstructures are between about 1μm and about 100 μm in size, and the refractive microstructures arebetween about 1 μm and about 100 μm in size. Moreover, the first andsecond patterns may be randomly and/or periodically arranged.

In some embodiments of the present invention, the refractive layer 130comprises an array of anamorphic lenses 132, as illustrated in FIGS. 1Aand 1B. Moreover, in FIGS. 1A and 1B, the spatial frequency of thereflective layer 120 is higher than the spatial frequency of therefractive layer 130. In other embodiments, however, this relationshipmay be reversed, as long as the first and second spatial frequencies aredifferent from one another.

Still referring to FIGS. 1A and 1B, the reflective layer 120 and therefractive layer 130 are arranged on the substrate 110, such that light142 that is projected to the front 102 of the projection screen 100passes through and is refracted by the refractive layer 130, to impingeon the reflective layer 120 and is reflected from the reflective layer120 back through the refractive layer 130 to emerge from the front ofthe projection screen 102. This refraction, reflection and refraction isshown by the light rays 144 a, 144 b that emerge from the front 102 ofthe projection screen 100.

Moreover, as also shown in FIGS. 1A and 1B, the projection screen has avertical axis V (FIG. 1B) and a horizontal axis H (FIG. 1A). Thereflective layer 120 and/or the refractive layer 130 are configured toproduce a vertical half angle θ_(V) of the light 144 b that emerges fromthe front 102 of the projection screen 100 that is less than ahorizontal half angle θ_(H) of the light 144 a that emerges from thefront 102 of the projection screen 110. This difference between thevertical half angle θ_(V) and the horizontal half angle θ_(H) isillustrated in FIGS. 1A and 1B by the larger horizontal half angle θ_(H)and light rays 144 a of FIG. 1A, compared to the smaller vertical halfangle θ_(V) and light rays 144 b of FIG. 1B.

In FIGS. 1A and 1B, the vertically extending grooves 122 that comprisethe reflective layer 120 and the anamorphic lenses that comprise therefractive layer 130, both can contribute to provide a smaller verticalhalf angle θ_(V) than the horizontal half angle θ_(H). However, in otherembodiments of the invention, uneven light distribution may be providedin opposite or different directions by the reflective layer 120 and therefractive layer 130, to provide a desired net light distribution. Thus,for example, in some embodiments of the invention, the grooves mayextend along the horizontal axis and/or the anamorphic lenses mayprovide a larger vertical half angle than a horizontal half angle.Stated differently, in some embodiments, as shown in FIGS. 1A and 1B,both the reflective layer 120 and the refractive layer 130 areconfigured to preferentially reflect or refract light along thehorizontal axis compared to the vertical axis. However, in otherembodiments, one of the reflective layer 120 or the refractive layer 130is configured to preferentially reflect or refract light along thehorizontal axis compared to the vertical axis, and the other of thereflective layer 120 or the refractive layer 130 is configured topreferentially refract light along the vertical axis compared to thehorizontal axis.

It also will be understood that, in FIGS. 1A and 1B, the substrate 110includes first 110 a and second 110 b opposing faces corresponding tothe front 102 and back 104 of the screen 100. In embodiments of FIGS. 1Aand 1B, the refractive layer 130 is on the first face 110 a, and thereflective layer 120 is between the refractive layer 130 and the firstface 110 a. However, in other embodiments of the invention, thesubstrate 110 may be transparent and the refractive layer 130 may be onthe first face 110 a, as shown in FIGS. 1A and 1B, but the reflectivelayer 120 can be on the second face 110 b corresponding to the back 104of the screen 100.

FIGS. 1A and 1B also illustrate specific embodiments of the presentinvention, wherein the projection screen 100 includes a substrate 110including a reflective metal face 110 a having a textured surface 120,to provide reflective microstructures 122 of about 0.5 μm to about 500μm in size, and arranged in a first pattern to reflect light at a firstspatial frequency. An array 130 of refractive microstructures 132 ofabout 0.5 μm to about 500 μm in size is provided on the textured surface120 and arranged in a second pattern that is different from the firstpattern to refract light at a second spatial frequency that is differentfrom the first spatial frequency. FIGS. 1A and 1B also illustrateembodiments of the invention wherein the projection screen has avertical axis (FIG. 1B) and a horizontal axis (FIG. 1A), and wherein thefirst pattern 120 comprises a plurality of grooves 122 that extend alongthe vertical axis (FIG. 1B), and wherein the refractive microstructures132 comprise a plurality of anamorphic microlenses having a verticalhalf angle θ_(V) that is less than a horizontal half angle θ_(H)thereof.

FIGS. 2A and 2B are cross-sections of projection screens according toother embodiments of the present invention, viewed from the top of thescreen and from a side of the screen, respectively. As shown in FIGS. 2Aand 2B, these projection screens 200 include a transparent substrate210. As used herein, the term “transparent” means that at least some ofthe light entering the substrate emerges from the substrate.

In embodiments of FIGS. 2A and 2B, the reflective layer 220 is on thesecond (back) face 210 b of the substrate 210, and the refractive layer230 is on the front face 210 a of the substrate 210. Moreover, inembodiments of FIGS. 2A and 2B, the reflective layer 220 comprises aplurality of anamorphic reflectors 222 having a vertical half angle thatis less than a horizontal half angle thereof, and the refractive microstructures 230 comprise a plurality of anamorphic microlenses 232 havinga vertical half angle that is less than a horizontal half angle thereof.Also, in embodiments of FIGS. 2A and 2B, the refractive layer 230 is afirst refractive layer, and the projection screen 200 further comprisesa second refractive layer 250 on the substrate 210. The secondrefractive layer 250 comprises refractive microstructures 252 of about0.5 μm to about 500 μm in size arranged in the first pattern. Thereflective layer 220 extends conformally on the second refractive layer250. As also shown in FIGS. 2A and 2B, the substrate includes first andsecond opposing faces 210 a and 210 b, respectively, the firstrefractive layer 230 is on the first face 210 a, the second refractivelayer 250 is on the second face 210 b, and the reflective layer 220 ison the second refractive layer 250 opposite the second face 210 b.

Accordingly, FIGS. 2A and 2B illustrate projection screens according toother embodiments of the present invention which comprise a transparentsubstrate 210 having front and back faces 210 a and 210 b, respectively.A first array 230 of refractive microstructures 232 of about 0.5 μm toabout 500 μm in size is provided on the front face 210 a, and arrangedin a first pattern to refract light at a first spatial frequency. Asecond array 250 of refractive microstructures 252 of about 0.5 μm toabout 500 μm in size is provided on the back face 210 b and arranged ina second pattern that is different from the first pattern to refractlight at a second spatial frequency that is different from the firstspatial frequency. A reflective layer 220 extends conformally on thesecond array of refractive microstructures 252, to provide an array ofreflective microstructures 222 of about 0.5 μm to about 500 μm in sizeon the back face 210 b and arranged in the second pattern to reflectlight at the second spatial frequency. Moreover, FIGS. 2A and 2Billustrate that the first 230 and second 250 arrays of refractivemicrostructures can comprise respective first and second arrays ofanamorphic microlenses having vertical half angles that are less thanhorizontal half angles thereof.

It also will be understood by those having skill in the art thatembodiments of FIGS. 1A, 1B, 2A and/or 2B may be combined in variouscombinations and subcombinations.

Additional discussion of various embodiments of the present inventionnow will be provided. In particular, as was described above, there maybe a tradeoff between brightness and field of view for a projectionscreen. Higher on-axis brightness may be achieved by reduction inbrightness at other angles. Thus, for a given projector 140 with a givenlumen output 142, a high gain screen may have a smaller field of view(half angle) than a low gain screen. Some embodiments of the presentinvention can at least partially overcome this potential tradeoff by ascreen construction that can limit only the vertical angle of view, butnot the horizontal angle of view.

Since viewers typically do not view the screen from large angles aboveor below the screen, light distributed into large vertical angles may bewasted. Accordingly, some embodiments of the invention can effectivelyharvest light that would otherwise be wasted in high vertical angles,and redirect this light into viewing angles that are generally used.Projection screens according to some embodiments of the presentinvention can, therefore, provide both high gain and high effectiveviewing angle, and can thereby appear to be much brighter than a whitewall, but without perceptible loss of horizontal viewing angle, and withonly modest loss of vertical viewing angle.

Some embodiments of the present invention can provide an array 130, 230of refractive microstructures 132, 232. The refractive microstructures132, 232 may be embodied as a microtextured light-diffusing surface madeof a transparent material. An array 120, 220 of reflectivemicrostructures 122, 222 also may be provided that, in some embodiments,comprises a metallic reflective material having a light directingmicrotexture on its outer surface. The array 130, 230 of refractivemicrostructures 132, 232 can be designed to cause diffusion of light 142as it arrives from the projector 140 onto the screen surface, and thenagain as light reflects from the array 120, 122 of reflectivemicrostructures 122, 222 back toward the viewer.

Many combinations of reflective and refractive microstructures may beprovided, according to various embodiments of the present invention, aslong as the reflective and refractive microstructures are of differentspatial frequencies. Thus, the refractive microstructures 132, 232 caninclude shapes that are designed to refract light into a desired rangeof angles. For example, the refractive microstructures 132, 232 cancomprise anamorphic microlenses having a fast and slow optical axis, sothat light is diffused into a larger range of angles in the plane of thefast optical axis (e.g., horizontally), and a smaller range of angles inthe plane of the slow optical axis (e.g., vertically). Thus, light maybe distributed more broadly in the horizontal direction than thevertical direction. In other embodiments, however, the refractivemicrostructures 132, 232 need not be lenses, and may or may not formdiscrete foci.

The array of reflective microstructures 122, 222, which may comprise ametal reflective layer, is designed to effectively reflect light fallingon its surface after passing through the refractive microstructures 132,232. In some embodiments, the array of reflective microstructures 122,222 may be provided by microtexturing, to produce additional divergenceof light as it reflects from the array of reflective microstructures122, 222. This additional diffusion can act independently of thediffusion that occurs in the refractive microstructures 132, 232. Thus,in some embodiments, the diffusion occurring in the reflectivemicrostructures 122, 132 may be cooperative with the diffusion occurringin the array of refractive microstructures 132, 232. However, in someembodiments, the diffusions may be opposite one another, or somecombination thereof. Accordingly, by combining the diffusion patterns ofthe refractive microstructures 132, 232, and the reflectivemicrostructures 122, 222, a field of view pattern may be produced thatis different from that which is provided by either set ofmicrostructures individually. The composite field of view may begoverned by a function that corresponds to a square root of the sum ofsquares of the individual fields of view, and that is independent foreach axis (horizontal or vertical) of the projection screen.

Generally, the structural elements that comprise the reflectivemicrostructures 122, 222 and the refractive microstructures 132, 232 mayhave discrete sizes ranging from about 0.5 μm to about 500 μm and, insome embodiments, from about 1 μm to about 100 μm. In some embodiments,the refractive microstructures 132, 232 may be in the form of concave orconvex microlenses of various size and shape combinations, or may beprism-like structures or multifaceted sections of various polyhedra,cylinders and/or aspheres, and combinations and subcombinations of theseshapes. The shapes may be random or regular across the surface of thescreen, and light distribution characteristics of such microstructuresmay vary in a random or regular manner across the surface of the screen.In addition to light distribution properties described above, therefractive microstructures 132, 232 may also provide an anti-glarecharacteristic to the screen due to the suppression or elimination ofspecular reflection, which can suppress or eliminate the effect ofambient light reflection. In some embodiments, the microtexturing of therefractive microstructures 132, 232 may be specifically selected toproduce strong diffusion of light in a horizontal direction (FIGS. 1Aand 2A), and weak diffusion of light in a vertical direction (FIGS. 1Band 2B). Moreover, in some embodiments, microtexturing shapes in therefractive microstructures 132, 232 may also be selected to causeasymmetric reflection along the vertical direction to allow for off-axisprojector placement.

The reflective microstructures 122, 222 may have the same or similarforms as the array of refractive microstructures 132, 232, but ofdifferent spatial frequencies as was described above. Moreover, thereflective microstructures may also be in the form of grooves, ridges,cross-hatching and the like. The array of reflective microstructures122, 222 may be of random, regular or quasi-periodic shape across thesurface of the screen, and light distribution characteristics of thereflective microstructures may vary in a random or regular manner acrossthe surface of the screen. In some embodiments, the microtexturing ofthe reflective microstructures 122, 222 may be specifically selected toproduce strong diffusion of light in the horizontal direction, withlittle or no diffusion of light in the vertical direction.

As was already described, the array of reflective microstructures 122,222 and the array of refractive microstructures 132, 232 are ofdifferent spatial frequencies. The different spatial frequencies may beprovided by dissimilar sizes, shapes, periodicities, and/or by providingaperiodic and/or quasi-periodic reflective and refractivemicrostructures. By providing different spatial frequencies, visiblemoiré or aliasing artifacts can be reduced or eliminated.

Fabrication methods for projection screens according to variousembodiments of the present invention now will be described withreference to FIGS. 3A and 3B. The following discussion will focus onembodiments of FIGS. 1A and 1B. However, similar techniques may be usedto fabricate embodiments of FIGS. 2A and 2B, or combinations andsubcombinations of these embodiments.

Referring to FIG. 3A, a surface 110 a of a reflective metal substrate110 is textured, to provide the array of reflective microstructures 122.The texturing may be performed in a variety of ways, includingmechanical techniques such as abrasion, brushing, chemical-mechanicalpolishing, sandblasting or the like; and/or by chemical techniques, suchas etching, anodizing and/or plating. In other embodiments, such as wasshown in FIGS. 2A-2B, metallization of a preformed microstructureproduced, for example, by microreplication, may be used to provide aconformal metal layer 220 on a microstructure array 250. Combinationsand subcombinations of these techniques also may be used. The metal maybe a highly reflective metal, such as aluminum, silver, chromium and/orother conventional reflective metals. In some embodiments, aluminum maybe used, and may be textured by an abrasive graining process, such asbrush finishing, as described, for example, in U.S. Pat. No. 3,964,822to Yamashita, entitled “Projection Screen and Process for ProductionThereof”, the disclosure of which is hereby incorporated herein byreference in its entirety as if set forth fully herein.

Referring now to FIG. 3B, a mold 360 of microlenses 362 (or, moreparticularly, an inverse of the microlenses) is arranged adjacent thesurface 110 a that was textured, with liquid photopolymer 370 betweenthe mold 360 and the surface 110 a that was textured, to thereby moldthe microlenses 362 in the liquid photopolymer 370. The liquidphotopolymer 370 is then photocured, and the mold 360 is removed. Itwill be understood that only partial curing of the liquid photopolymermay take place by photoexposure and remaining curing may take placeusing other techniques, such as heating.

In some embodiments, the mold 360 is placed adjacent the surface 110 athat was textured, and the liquid photopolymer 370 is then injectedbetween the mold 360 and the surface 110 a that was textured. In otherembodiments, the liquid photopolymer 370 is placed on the surface 110 athat was textured, and the mold 360 is then placed on the liquidphotopolymer 370. The mold 360 may be fabricated, for example, bymicroreplication of a master containing the desired shapes that make upthe microtexture. The mold may be fabricated, for example, as describedin Published United States Patent Application Nos. US 2005/0058947 A1 toRinehart et al., entitled Systems And Methods for Fabricating OpticalMicrostructures Using a Cylindrical Platform and a Rastered RadiationBeam; US 2005/0058948 A1 to Freese et al., entitled Systems and Methodsfor Mastering Microstructures Through a Substrate Using NegativePhotoresist and Microstructure Masters So Produced; and/or US2005/0058949 A1 to Wood et al., entitled Systems and Methods forFabricating Microstructures by Imaging a Radiation Sensitive LayerSandwiched Between Outer Layers, and Microstructures Fabricated Thereby,all published Mar. 17, 2005, and assigned to the assignee of the presentinvention, the disclosures of which are hereby incorporated herein byreference in their entirety as if set forth fully herein.

A transparent or semitransparent material, such as the photopolymer 370may be used. Dyes or colorants may be added to the photopolymer 370 inorder to impart a specific color and/or to change the color renditioncharacteristics of the screen. Diffusive materials also may be added tothe photopolymer 370 in order to modify its diffusive properties. Aspecific hardness property may be chosen for the photopolymer 370, sothat the finished screen may have scratch resistant properties. Variousconventional bulk and/or surface treatments also may be applied. Forexample, a conventional staticide may be used to impart anti-staticproperties to layer.

FIGS. 4A and 4B are micrographs of a portion of a projection screen ofFIGS. 1A and 1B that was fabricated as was described in FIGS. 3A and 3B.In particular, FIG. 4A illustrates the texturing of a metal substrateusing grooves, as was shown schematically in FIG. 3A. FIG. 4Billustrates the microlenses 362 of FIG. 3B on the grooved metalsubstrate of FIG. 4A.

EXAMPLE

The following Example shall be regarded as merely illustrative and shallnot be construed as limiting the invention.

A front projection screen was constructed from two attached layers. Thefirst layer, corresponding to the substrate 110 and the array ofreflective microstructures 122 of FIGS. 1A and 1B, was produced bystarting with a 0.001″ thick aluminum sheet whose surface was grained inone direction using a brush finishing technique. This produced a surfaceincluding random parallel grooves and ridges of about 5 μm in width,with a depth of about 1 μm. See FIG. 4. The textured surface was primedwith a transparent primer layer of acrylic primer and dried.

To form the array of refractive microstructures 132, a photopolymermicrolens mold 360 was placed in contact with the primed surface, andthe space between the mold 360 and the primed aluminum surface 122 wasfilled with liquid photopolymer 370 by injection. The liquidphotopolymer that was used was Sartomer PRO 7590 acrylic photopolymer.Excess photopolymer 370 was squeezed out using a laminator. The laminatewas exposed through the transparent mold 360 to ultraviolet light, witha wavelength of about 360 nm and an intensity of about 200-300watt/inch, to cure the photopolymer 370. The mold 360 was then removed,to leave a replica of the microlenses attached to the primed surface ofthe aluminum.

In the present Example, the microlenses 132 were chosen to have a veryhigh optical divergence in a horizontal direction and a smaller opticaldivergence in the vertical direction. In particular, the microlenses 132were anamorphic microlenses with a horizontal base of 80 μm, a verticalbase of 20 μm, and a depth of 40 μm. The grain pattern in the aluminumwas oriented such that the grains were parallel to the vertical axis, asshown in FIG. 1B, thus further enhancing horizontal optical divergenceof the composite structure. As shown in FIGS. 1A and 1B, light 142arriving from the projector 140 strikes the array of refractivemicrostructures 132, and is strongly diverged in a horizontal directionand weakly diverged in a vertical direction towards the array ofreflective microstructures 122. Light striking the reflectivemicrostructures 122 is further diverged in the horizontal direction, butnot diverged in the vertical direction on reflection due to the surfacegrain pattern. Light reflected from the reflective microstructures 122again pass through the refractive microstructures 132 and again isstrongly diverged in a horizontal direction and weakly diverged in avertical direction. The resulting light distribution provides a verywide horizontal field of view and a much smaller vertical field of view.By restricting the vertical field of view, the on-axis gain of thescreen can be increased. Specifically, in the present Example, thereflective microstructures have a horizontal half angle of 11° and avertical half angle of 5°. The refractive microstructures 130 have ahorizontal half angle of 22° and a vertical half angle of 17°. Thecomposite screen showed an on-axis gain of 2.4, a horizontal half angleof 35° and a vertical half angle of 15°. In addition, the screen of thisExample showed very low glare and good scratch resistance.

In the drawings and specification, there have been disclosed embodimentsof the invention and, although specific terms are employed, they areused in a generic and descriptive sense only and not for purposes oflimitation, the scope of the invention being set forth in the followingclaims.

1. A projection screen comprising: a substrate; a reflective layer onthe substrate; and a refractive layer on the substrate, the refractivelayer comprising an array of anamorphic microlenses; wherein theprojection screen has a front and a back and wherein the reflectivelayer and the refractive layer are arranged on the substrate such thatlight that is projected to the front of the projection screen passesthrough and is refracted by the refractive layer to impinge on thereflective layer and is reflected from the reflective layer back throughthe refractive layer to emerge from the front of the projection screen;and wherein the projection screen has a vertical axis and a horizontalaxis and wherein the reflective layer and/or the refractive layer areconfigured to produce a vertical half angle of the light that emergesfrom the front of the projection screen that is less than a horizontalhalf angle of the light that emerges from the front of the projectionscreen.
 2. A projection screen according to claim 1 wherein theanamorphic microlenses are about 0.5 μm and about 500 μm in size.
 3. Aprojection screen according to claim 1 wherein the substrate includesfirst and second opposing faces, wherein the refractive layer is on thefirst face and wherein the reflective layer is between the refractivelayer and the first face.
 4. A projection screen according to claim 1wherein the substrate includes first and second opposing faces, whereinthe refractive layer is on the first face and wherein the reflectivelayer is on the second face.
 5. A projection screen according to claim 1wherein the anamorphic microlenses are between about 1 μm and about 100μm in size.
 6. A projection screen according to claim 1 wherein thearray of anamorphic microlenses are randomly and/or regularly arranged.7. A projection screen according to claim 1 wherein the array ofanamorphic microlenses is a first array of anamorphic microlenses andwherein the projection screen further comprises a second array ofanamorphic microlenses on the substrate.
 8. A projection screenaccording to claim 7 wherein the substrate includes first and secondopposing faces, wherein the first array of anamorphic microlenses is onthe first face and wherein the second array of anamorphic microlenses ison the second face.